The present invention relates to a sphygmomanometer, which is concurrently capable of detecting arrhythmia, or pulse irregularities. More particularly, it relates to an instrument for detecting and indicating the Korotkoff sounds for the purpose of measuring blood pressure, which concurrently functions as a detector and as an indicator of arrhythmia.
Often during general medical check-up or diagnosis blood pressure is measured with a sphygmomanometer. It is of course an indispensable step during medical examinations of elderly patients.
If blood pressure and arrhythmia which is closely related with the blood pressure trend can be measured simultaneously with a single instrument or apparatus, it would be very convenient and would contribute much to the improvement of the medical examination. No conventional sphygmomanometer is known capable of easily detecting the arrhythmia. None of the known arrhythmia detecting instruments is capable of measuring the blood pressure simultaneously.
Blood pressure has been traditionally determined by measuring the maximum and minimum value thereof employing an indirect method of listening to the appearance and disappearance of the so-called Korotkoff sounds. A kind of elongated air bag called a cuff is wound around an arm of a human body and air is sent thereinto to build up a pressure until the blood flowing in the artery is stopped, and then the air pressure is gradually decreased. At some point Korotkoff sounds (i.e. frictional sounds between the artery wall and the flowing blood) begin to be heard when the systolic blood pressure is measured. Afterwards, the air pressure is further decreased until the Korotkoff sounds disappear which is the point when the diastolic blood pressure can be measured.
Pulses including Korotkoff sounds of such type can be usually collected by a pulse detector or sensor with a microphone (called a pick-up), to be electrically transformed into a wave signal of the vascular pulse wave. As a pulse detector, U.S. Ser. No. 722,122 "Vascular Sound Detector", now U.S. Pat. No. 4,141,350 to Shinoda et al. which has been assigned to the same assignee as that of the present application, or other disclosures can be seen. The output from this kind of detector in a form of a wave signal is electrically treated for furnishing Korotkoff sounds, in a separate or recognizable form, which enables the measurement of the blood pressure desired to be performed.
Sphygmomanometers of such a structure are disclosed and some of them are already on the market. By way of example, TOKU-KAI-SHO-No. 52 (1977)-84886 (Japan), "Sphygmomanometer", which has been assigned to the same assignee to that of the present application, is a device wherein pulse-sound-signal and Korotkoff-sound-signal (frictional sound between the artery wall and the flowing blood) can be selected or separated according to the form of the vascular pulse wave, and the two types of wave signal are led through an electronic circuit to two differently colored light emitting diodes. This instrument is capable of indicating, for example, the pulse sound signal in red and the Korotkoff sound signal in blue, i.e., indicating by color the appearance and the disappearance of Korotkoff sounds, the diastolic and systolic blood pressure being indicated on a visually readable numerical display.
Another example, TOKU-KAI-SHO-No. 52 (1977)-84885 (Japan), "Indicator for short of pressure-rising in an Automatic Sphygmomanometer" which has been assigned to the same assignee to that of the present application, is of a mechanism, wherein the cuff pressure can be automatically and progressively raised until it reaches a suitable pressure for initiating measurement of the blood pressure.
On the other hand, various instruments or devices are already disclosed as to the recognition of the arrhythmia, such as frequent pulses, and infrequent pulses, and irregular pulses. Against the normal pulsation rhythm, a repeated dual-type pulsation of 60 to 80 times per minute, pulsation more than 100 per minute is defined as frequent, pulsation less than 50 per minute infrequent, and other irregularities, for instance, triple or quadruple rhythm are also defined as arrhythmia in a narrow sense.
Instruments for detecting arrhythmia are generally so deigned as to perform electrical detection of pulsation irregularities by means of electrically comparing the period of vascular pulsation of a subject with a predetermined criterion or standard, i.e., by electrically detecting the degree of deviatin from the criterion.
Taking an interval of two neighboring pulsations, or an average interval of several consecutive pulsations, as a standard value for converting it into a clock pulse number of a certain frequency, and two values calculated by adding and substracting one to and from every N clock pulses shall be memorized by a memory storage as the upper and lower limits for the jugement. The arrhythmia is judged by comparing the clock pulse number of the next pulse interval with this criterion. Another way of discovering an arrhythmia is enacted by letting a memory storage memorize in advance a standard period or cycle of the pulse signal (for example in a form of clock pulses) corresponding to a vascular pulse, after increasing or decreasing by a certain percentage to and from the standard pulse number for setting the upper and lower limits for the comparison, i.e., a window comparator. Comparing the pulse signals with the standard frame set on the window comparator, arrhythmia can be recognized.
As above-mentioned, sphygmomanometers as such and detectors of arrhythmia respectively have been developed so far. In both fields various excellent instruments have been disclosed and provided on the market. As an individual instrument most of them are satisfactory. Combined instruments capable of functioning in two ways, i.e., adapted to accomplish both objects, have never been developed heretofore, despite the fact that the individual mono-purpose devices are excellent and despite the fact that both instruments are used during one examination of one patient quite often.